Mineral exploration

ABSTRACT

A method and apparatus for mineral, in particular hydrocarbon exploration in which determination is made of whether substances indicative of a deposit are present in the atmosphere in the form of charges, molecules or clumps of molecules. Intaken air is purged of particles and only small naturally charged molecules or clumps are transferred to, for instance, an inert gas for spectroscopic examination.

DESCRIPTION

This invention relates to mineral exploration, in particular, though notexclusively, exploration to locate hydrocarbon, that is oil and naturalgas, deposits.

For some time now efforts have been made to locate mineral deposits, inparticular hydrocarbon deposits of oil and natural gas, by traversing anarea of the sea or land which is to be explored in a vehicle such as anaeroplane, and collecting particles which are in suspension in theatmosphere. The idea is that particles above, or down wind of, a depositwill display abnormally high concentrations, which are referred to asanomalies, of elements in or associated with the deposit. Such ananomaly arises, it is thought, by the elements being present upon theparticles as adsorbed coatings, and in the context "coating" includescases where individual or a number of atoms or molecules adhere to theparticle surface, as well as cases of a complete or substantial coveringof the particle. The coatings are taken to be representative of thegeochemical and other characteristics of the area, and the coatings,particularly of larger particles, which are expected to have travelledless far from the source before losing or changing their coatings, canbe, and in common practice are, analysed. There are various batchmethods of making such analysis, although these are rather slow andunreliable and have to be performed some time after the particles arecollected. An alternative and continuous method of analysis which can beperformed for instance in an aeroplane is spectroscopy, such asemission, absorption or mass spectroscopy. Thus, it has been proposed tointroduce collected particles directly into a plasma and examine thespectrum of light emitted. In order to reduce the problem ofinterference between individual weak spectral lines attributable to thecoatings and strong lines attributable to the particles, and the problemthat there may be a variable thermal load in the plasma due tovariations in the number of particles collected and their size, and asthe larger particles tend to interfere with the field of view, it hasfurther been proposed to volatilize the coatings in a first plasma andcarry the volatilized coatings, but not the particles, into a secondplasma in which the spectrum of light from the coating is observed. Thesecondary plasma has a more constant thermal load than the first, itallows a better field of view and the emitted light can more readily beviewed by a spectroscope and subjected to normal spectroscopic analysis.

In connection with exploration for hydrocarbon deposits, it has recentlybeen suggested that, using this technique of examining particlecoatings, one should look not only for hydrocarbons themselves, oranomalous spectral lines attributable thereto, but also, oralternatively, for anomalies of the gas radon and/or a halogen, notablyiodine. A first reason for this is that the usual hydrocarbon spectralbands can be rather easily confused with the lines of unrelatedcompounds. A second reason is that halogens (particularly iodine) anduranium are always present anomalously in hydrocarbon deposits. Uraniumdecays to radium, which decays to inter alia, radon gas (atomic number88, atomic weight 222). Thus, simultaneous anomalies or radon and/oriodine and hydrocarbon suggest a hydrocarbon deposit much morepositively than a mere hydrocarbon anomaly which might arise for otherreasons. To date, however, such proposals have been restricted to theconsideration of particle coatings and at present all efforts in thisfield are directed to the analysis of particle coatings.

It is now believed that it may not be necessary, and indeed isundesirable, to collect airborne particles and investigate theircoatings. On the contrary, it is now considered that there is evidencefor supposing that molecules representative of a deposit are present inthe atmosphere above the deposit, unattached to particles, probably inclusters or "clumps" of up to 30 molecules or more. These are, it is nowbelieved, charged, but only retain the charge for a short time becauseof collisions with ions of opposite charge or adsorption onto dustparticles. It is believed these molecules or clumps are dispersedupwards in the atmosphere by rising currents of air and predominantly bythe force of the earth's electric field. While it can not be said thatthey are not present as coatings on atmospheric particles such as dustor salt particles, it is believed that they exist as such, unattached.Moreover, it is believed that at least in the case or hydrocarbondeposits, the molecules or clumps are negatively charged. It is notknown why this should be so, but it seems possible that as the uraniumin the deposit decays α-particles ionise molecules which, in the courseof their movement form the clusters or clumps which are negativelycharged. These pass to and through the earth's surface as negative ions.

In its first and broadest aspect, therefore, the present inventionprovides a method of mineral exploration by traversing an area to beexplored and determining whether substances indicative of a mineraldeposit are present to an anomalous extent in the atmosphere in the formof charged molecules or charged clumps of molecules.

The invention more particularly provides a method of exploration bytraversing an area to be explored and determining whether substancesindicative of a hydrocarbon deposit are present to an anomalous extentin the atmosphere in the form of charged molecules or charged clumps ofmolecules.

In the case of exploration for hydrocarbon deposits, the substances tobe detected will be hydrocarbons and preferably also halogens, inparticular iodine, and/or uranium or more exactly, a product of uraniumdecay, in particular the gas radon. Exploration will preferably beconducted in an aircraft and detection will preferably be conducted byspectroscopy, preferably emission spectroscopy and, desirably, in theaircraft so that continuous monitoring can be performed.

In performing this method, samples of air may be collected in thevehicle, for instance through a special intake at the front of anaircraft, and it is preferable to collect and/or pass the air throughone or more devices which concentrate the molecules and preferably alsoreject extraneous matter such as dust and insects. To these ends, aircan be collected through an electrostatic focussing tube or an aerodynetube which is insulated and arranged to give a focussing effect and itis preferably then passed through a centrifuge such as a cyclone inorder to concentrate and discharge extraneous matter. For instance,particles greater than 0.5 to 1 μm in size can be rejected. While it ispreferable to employ at least one of the aerodyne tube and centrifuge,there may be circumstances in which neither is strictly required. Theair can be stored for later analysis or, more preferably, particularlyas radon decays quite rapidly (it has a half life of about 3.7 days) themolecules are immediately subject to analysis preferably byspectroscopic analysis. Arrangements can be made to relate the resultsof the analysis with the particular geographical position at which thesample concerned was taken, as has been done before in the analysis ofparticle coatings. However, as it is believed the charges dissipaterelatively rapidly, the results obtained will be characteristic of theimmediate area of collection, in contrast to known methods based onparticle collection which required an estimate of displacement.

In order to perform spectroscopic analysis to detect anomalies in theoccurence of such molecules or clumps, it is necessary to transfer themolecules from the air in which they are collected into an inert gas bywhich they are passed to a zone in which the plasma is formed.

When, according to the former exploration techniques, particle coatingswere analyzed by spectroscopy, one method of performing such transferwas to pass the collected air, after cyclonic concentration of theparticle content, to a device which provided for the air flow to meet anopposite flow of the inert gas, whereon the air was drawn off to oneside and some of the particles continued, due to their momentum, throughthe "barrier" of the inert gas into a second flow of inert gas in thesame direction as the original air flow. By the second flow, theparticles are carried to the plasma zone. During their passage theparticles can be counted in a particle counter if desired. The inert gasis, for this purpose, fed to a tube which is coaxial with the air tubeand in which the inert gas flows on the one hand towards the air tube soas to form the barrier and also in another stream away from the air tubeto carry transferred particles to the plasma zone. The various flowswere adjusted so that only larger particles, which are expected to bemore representative of the locality, for instance those exceeding 30microns or even 10 or 5 microns in diameter, are carried through theplasma zone, the rest being repelled at the barrier and being drawn offwith the air.

It is not possible directly to apply this technique to the transfer ofmolecules or clumps from air to an inert gas because the molecules willhave insufficient momentum to penetrate the barrier, which must be of atleast a few centimeters in length in order to ensure that the air doesnot enter the plasma zone. Moreover, of course, some particles willinevitably remain in the airstream even after centrifuging and thesemust be repelled at the barrier in order to put the invention intoeffect.

It is proposed to overcome this difficulty by taking advantage of thefact that the molecules or clumps are charged. Thus, according to asecond aspect of the invention it is proposed that the charged moleculesbe transferred from the air in which they are collected to an inert gasby causing the air and inert gas to meet at a boundary at which there isan interface between the air and the inert gas, and causing the chargedmolecules to traverse the interface into the inert gas by theapplication of electrical or magnetic fields.

The air will be withdrawn from the region of the interface. In apreferred method it is arranged for a first stream of inert gas to flowtowards the interface and counter to the air flow and for a secondstream of inert gas to be further from the interface and to flow awayfrom it, in the same direction as the air flow.

Thus, the first inert gas stream "seals" subsequent parts of theapparatus against ingress of air and particles, and the molecules arecaused to traverse the seal in order to be carried by the second streamto a plasma zone.

It is also proposed to provide apparatus in which charged molecules canbe transferred from air to an inert gas and comprising a first, airguide, tube through which in use collected air is passed, a second,inert gas, tube through which inert gas can be supplied to meet the airat a boundary at which there is an interface between the air and theinert gas, and electrical or magnetic means for causing the chargedmolecules in the air to traverse the interface into the inert gas.

Preferably, the tubes are arranged so that the air and a first stream ofinert gas flow towards one another at the interface and there is asupply of inert gas to form that first stream and a second stream whichflows in the same direction as the air from a position downstream of theinterface in the original direction of air flow. Thus, the inert gas canbe supplied to the second tube through an inlet spaced from the end ofthe tube adjacent the air tube, in the two streams, which flow away fromone another. In use, the second stream of inert gas carries transferredcharged molecules towards a plasma zone where a plasma can be createdand spectroscopic analysis performed.

Alternatively the tubes can be side by side with an aperture from one tothe other to provide the interface.

The means to transfer the charged molecules across the barrier can takea wide variety of forms, for instance appropriately positioned magneticcoils with stationary or oscillating magnetic fields can be provided orelectrodes with means for charging them can be located at suitablepositions. One particularly convenient way of causing the transfer is toemploy the air flow through the air tube itself to generate a negativeelectrostatic charge on the tube, and this can be done by including inthe tube, which is otherwise of an insulating material, a part which isconductive and which is insulated. If, for instance, this part convergesto a sharp edge at the end of the tube, then the frictionally developedcharge will tend to concentrate at that edge and the fields created cancause the charged molecules to be concentrated in the centre of the tubeand to be projected across the interface into the inert gas, rather thanbe carried further along by the air flow. It is strongly preferable,indeed it is probably essential for practical purposes, for a part ofthe inert gas tube remote from the barrier also to be of a conductivematerial, preferably earthed, for instance to the airframe if anaeroplane is employed.

A result of the invention is that only molecules or clumps which arenaturally ionised and, it appears, naturally charged, are in generalcollected.

In addition to the above mentioned aspects independently, the inventionprovides a method of mineral exploration involving traversing an area tobe explored and determining whether substances indicative of a mineraldeposit are anomalously present in the atmosphere in the form of chargedmolecules or clumps of molecules, the method involving collecting airand transferring the charged molecules from the air to an inert gas forthe purpose of spectroscopic analysis by causing the air and inert gasto meet at a boundary at which there is an interface between the air andthe inert gas, and causing the charged molecules to traverse theinterface into the inert gas by the application of electrical ormagnetic fields.

The invention further provides apparatus for use in such a methodcomprising means to be mounted on a vehicle and to collect air, suchmeans being connected to a first, air guide tube through which in usecollected air is passed, a second, inert gas, tube through which inertgas can be supplied to meet the air at a boundary at which there is aninterface between the air and the inert gas, and electrical or magneticmeans for causing the charged molecules in the air to traverse theinterface into the inert gas. Such apparatus may, of course, includemeans for forming a plasma and performing spectroscopic analysis, andmay also include an aerodyne tube to collect the air, and a centrifugeto rid the air of particles and extraneous matter.

Any aerodyne may be in the form of an inlet which converges in thedirection of incoming air flow and is formed of a plurality of baffles.Such arrangements are already known, but according to a preferredfeature it is further proposed that the baffles be conductive and bemounted in an insulating manner. If this is done, frictionally generatednegative charge on the baffles will tend to concentrate chargedmolecules centrally of the inlet, particularly when the apparatusincludes an earthed member downstream of the baffles.

An alternative inlet arrangement has a conical, insulated wire mesh,converging in to inlet direction and connected, in insulating manner toan intake tube. This mesh will become negatively charged, by airfriction, and force small molecule clumps, but not large ones or anyparticles, towards the centre so that they pass down the tube. Othermatter passes through the mesh and is discharged.

In a cyclone or centrifuge, the inside walls will be charged by airfriction so as to concentrate the charged molecules in the centre; theyare then ejected from the narrow, light fraction end in a cyclone. Acascade of cyclones can be employed.

In order that the invention may be more clearly understood the followingdescription is given by way of example only with reference to theaccompanying drawings in which:

FIG. 1 is a schematic side view of apparatus for collecting air andperforming spectrometry on molecules and ions entrained therewith;

FIG. 2 is a more detailed sectional view of part of the apparatus FIG.1.

As shown in FIG. 1, apparatus which may be located in an aircraftincludes an air intake 2 which will project out of the aircraft tocollect air, and is in the form of an aerodyne tube, or preferably andas shown, of a tube with a conically convergent insulated wire meshtherein, leading to a cyclone 3 for differentially concentratingparticulate matter towards the outside for discharge, and a tube 6 bywhich the air and charged molecules are conducted to a device 7 at whichthe charged molecules are transferred from the air to an inert gassupplied to an inlet chamber 10 by a tube having a valve 11, andentering from the inlet chamber 10 into tubes 8 and 9. The inert gasflows in the tube 8 towards the air flow and forms a barrier therewithin the tube 8 and the air, which is stopped in its original direction offlow, is exhausted from the device 7 by a fan 5; charged molecules inthe air, however, are caused to traverse the barrier of inert gas byelectrical or magnetic means and enter the tube 9 in which there is aninert gas flow in the same direction as the original air flow in tube 6and which conducts the molecules to a plasma zone 15 in which, forinstance by means of two electrodes, a plasma (preferably D.C) isgenerated which can be viewed through a spectrometer or monochrometer17. The output of this is processed and recorded by an electronic device18 coupled to a navigating system 19 so that the output of thespectrometer or monochrometer can be correlated with the position of theaircraft over the ground. Of course the plasma need not be an electrodeplasma, radio frequency or microwave plasmas can be used instead ifdesired and indeed mass spectroscopy could be employed. A further pump12 draws the inert gas through the plasma at a rate controlled by avalve 16, which should give a constant flow.

In order to cause the charged molecules to traverse the barrier from theair flow into the inert gas an electromagnetic arrangement, for instancecoils surrounding the molecule path, can be provided. Alternatively anelectrostatic arrangement can be employed. FIG. 2, which is a moredetailed view of part of the apparatus of FIG. 1, shows one suchelectrostatic arrangement.

In this arrangement, the air inlet tube 6 has a terminal portion 20which is of a conductive material and is mounted in an insulatingmanner. This terminal portion 20 is surrounded by a shroud 27 of thedevice 7 which has an outlet leading to the fan 5 of FIG. 1. Alignedwith the portion 20 is the tube 8 which is in turn aligned with the tube9 and between the tubes 8 and 9 are orifices of inlet conduits 23 forinert gas supplied from the chamber 10. Beyond the inlet orifices is afurther conductive part 24 of the tube 9 electrically connected to ashroud 27. However, the portion 20 is the only part of the apparatusillustrated in this Figure which has to be of conductive material. Inuse, the air flow through the tube 6 and any particles therein meet andare stopped by an opposite flow of inert gas in the tube 8 suppliedthrough the conduits 23. Thus, the air flow should not be so great, orthe inert gas flow so low, that particles or air are transferred.

The air is exhausted through the shroud 27 by the fan 5. Downstream ofthe orifices of conduits 23 the inert gas flow is in the same directionas the original air flow so as to carry charged molecules which traversethe barrier between the air and inert gas to subsequent stages. The airflow over the portion 20 and shroud 27 cause them to be negativelycharged by friction and the charges developed on portion 20 migrate to alarge extent to the point 21 which is made as sharp as possible.Provided therefore that the charged molecules are carried by the airflow up to the point 21, the charge at that point will cause them tocontinue in their path despite the reversal in the air flow. The effectis enhanced by the conductive part 24 by reason of which a strongelectric field will exist between parts 20 and 24 which the chargedmolecules will be unable to cross. Thus, the charged molecules traversethe barrier and pass through the counterflow of inert gas into the flowof inert gas in the tube 9. The portion 20 is also, as shown, providedwith a second sharp end 22 and while charge will accumulate here alsothe construction and air flow can readily be made such that the chargehere acts to centre the charged molecules in the air flow rather than toprevent their flow through the portion 20.

The FIG. 2 arrangement as described so far is in effect a simple butautomatic arrangement for transferring charged molecules from the airflow to the inert gas flow but it can be improved or modified by simplyarranging for selected potentials to be applied to the portion 20 and ifdesired the part 24. The portion 20 could be biased to increase ordecrease the rate of charged molecule transfer to the inert gas and inthis case it might not be necessary to shape the portion 20 as it isshown in FIG. 2. Similarly, part 24 could be biased as desired to affectthe charged molecule flow through the tube 9. It will normally bedesirable to prevent airborne particles which are collected at the sametime as the charged molecules from being transferred into the inert gasand thence to the plasma. To a large extent this can be arranged by thecentrifuge already described which can separate down to 1 μm, but inaddition can be affected by adjusting the air and inert gas flows in thetubes 6 and 8 and by appropriate selection of the lengths of tubes 8 and9. In addition a particle collector could be located in the tube 9 andif desired a particle counter can be included in the tube 9 to assessthe effectiveness of the measures taken to keep particles out of thetube. Such a counter can be constructed as an interruption in the tube 9surrounded by an inert gas containing chamber and in which a light beamcan be employed in a known manner with a photoelectric device to countparticles crossing the gap. To protect the plasma zone further from thepresence of undesired particles, a filtering arrangement can be employedbetween the tube 9 and the plasma zone, such as a thermostaticallycontrolled oven enclosing a sintered porous filter to collect anyparticles which are inadvertently transferred into the inert gas andconveyed to that point. The oven is heated to prevent the adsorption ofthe charged molecules on the filter; it facilitates the transport of themolecules to the plasma and the resultant pre-heating of the gasfacilitates the operation and striking of the plasma, but this may notbe necessary.

A grid can be provided at the interface between air and inert gas, withbiasing means so as to shut off or encourage charged molecule flow in acontrolled manner.

It will be appreciated that the practice of this invention is based onthe belief that the molecules or clumps are charged. If this is correct,then under fair weather conditions the clumps or molecules willgenerally travel straight upwards due to the earth's electric field.This belief is reinforced by the fact that it is found that inconditions where the electric field of the earth is disturbed, e.g. atcold fronts, sea mists and thunderstorms, the invention cannot beefficiently practised because the number of such molecules or clumps tobe collected is significantly reduced.

I claim:
 1. A method of mineral exploration which comprises the stepsof: traversing an area to be explored; sampling atmospheric air whileconducting such tranverse; separating charged molecules and chargedclumps of molecules from such sampled air; determining the extent towhich substances indicative of a mineral deposit are present in suchcharged molecules and charged clumps of molecules and determiningwhether such substances are present to an anomalous extent indicative ofa mineral deposit.
 2. A method as claimed in claim 1 in which thecharged molecules and charged clumps of molecules are separated from theair by transferring them to an inert gas stream from the air, suchtransfer being effected by causing the air and inert gas to meet at aboundary at which there is an interface between them through whichparticulate matter in the air will not pass, and applying an electricalor magnetic field to cause the charged molecules to traverse theinterface into the inert gas.
 3. A method as claimed in claim 2 whereinthe air and a first stream of inert gas are caused to flow towards theinterface from opposite directions, the air is withdrawn from theinterface, and a second stream of inert gas is flowed away from theinterface from a position removed from the interface.
 4. A methodaccording to claim 3 wherein the air is fed towards the interfacethrough a tube which terminates adjacent the interface, at least a partof the tube being of insulated conductive material.
 5. A methodaccording to claim 1 including the step of correlating the determinationwith the immediate position in the traverse.
 6. A method of explorationwhich comprises the steps of: traversing an area to be explored;sampling atmospheric air while conducting such traverse, separatingcharged molecules and charged clumps of molecules from such sampled air;determining the extent to which substances indicative of a hydrocarbondeposit are present in such charged molecules and charged clumps ofmolecules and determining whether such substances are present to ananomalous extent indicative of a hydrocarbon deposit.
 7. A method asclaimed in claim 6 wherein the substances in respect of whichdetermination is made are hydrocarbons.
 8. A method as claimed in claim6 wherein the substances in respect to which determination is made arehalogens, in particular iodine.
 9. A method as claimed in claim 6wherein the substances in respect of which determination is made are atleast one of uranium and products of uranium decay in particular radon.10. A method as claimed in claim 6 wherein the step of sampling includesthe steps of collecting air through an intake of an aircraft in whichthe traverse is conducted, and concentrating the charged molecules orclumps and rejecting extraneous matter prior to the step of separationof charged molecules and charged clumps of molecules.
 11. A method asclaimed in claim 10 wherein the step of concentration is conducted usingat least one of: an aerodyne tube; an inlet provided with an insulatedconvergent wire mesh leading to a pipe; and a centrifuge, such as acyclone; and wherein particulate matter in excess of 1 micron in size isrejected.
 12. A method as claimed in claim 6 wherein the step ofdetermination is conducted by spectroscopy, in particular emissionspectroscopy.
 13. A method of mineral exploration which comprises thesteps of: traversing an area to be explored; collecting atmospheric airduring such traverse, separating particulate matter from the collectedair; transferring charged molecules and charged clumps of molecules fromthe air to an inert gas, such transfer being effected by causing the airand inert gas to meet at a boundary at which there is an interfacebetween the air and the inert gas, applying an electrical or magneticfield to cause the charged molecules and charged clumps of molecules totraverse the interface into the inert gas, spectroscopically analysingthe molecules and clumps so transferred, determining the extent to whichsamples indicative of a mineral deposit are present in such moleculesand clumps and determining whether such substances are present to ananomalous extent indicative of a mineral deposit.
 14. A method ofexploration which comprises the steps of: traversing an area to beexplored; collecting atmospheric air during such traverse, separatingparticulate matter from the collected air; transferring chargedmolecules and charged clumps of molecules from the air to an inert gas;such transfer being effected by causing the air and inert gas to meet ata boundary at which there is an interface between the air and inert gas,applying an electrical or magnetic field to cause the charged moleculesand clumps of molecules to traverse the interface into the inert gas,spectroscopically analysing the molecules and clumps so transferred,determining the extent to which samples indicative of a hydrocarbondeposit are present in such molecules and clumps, and determiningwhether such substances are present to an anomalous extent indicative ofa hydrocarbon deposit.
 15. Apparatus for use in mineral, in particularhydrocarbon, exploration by traversing an area to be explored, suchapparatus comprising means defining an intake for sampling air; acentrifuge to concentrate charged molecules and charged clumps ofmolecules occuring in the sampled air and to reject extraneous matterfrom the air; means to separate the concentrated charged molecules andcharged clumps of molecules from such sampled air; and means fordetermining the extent to which substances indicative of a mineraldeposit are present in such charged molecules and charged clumps ofmolecules.
 16. Apparatus according to claim 15 and further comprising,as the intake, one of: an aerodyne tube having baffles of conductivematerial mounted in an insulating manner, and a conduit providedinternally with an insulated convergent wire mesh leading to a pipe. 17.Apparatus as claimed in claim 15 including a spectrometer with which thedetermination is performed.
 18. Apparatus as claimed in claim 15including means to transfer charged molecules and charged clumps ofmolecules from the air to an inert gas, such means including a first,air guide passage through which in use collected air is passed, asecond, inert gas passage through which in use an inert gas can besupplied to meet the air at a boundary at which there is an interfacebetween the air and inert gas, and means for applying one of anelectrical and magnetic field for causing the charged molecules in theair to traverse the interface into the inert gas.
 19. Apparatus asclaimed in claim 18 wherein said passages are so arranged that in usethe air and a first stream of inert gas flow towards one another at theinterface and including means to provide a first supply of inert gas toform that first stream and a second supply of inert gas which flows inthe same direction as the air from a position downstream of theinterface in the original direction of air flow.
 20. Apparatus asclaimed in claim 19 wherein said air passage terminates adjacent theinterface, at least a part of said passage being of insulated,conductive material.
 21. Apparatus for use in mineral, in particularhydrocarbon, exploration by traversing an area to be explored, suchapparatus being locatable on a vehicle and comprising in combination anintake for sampling air, means for rejecting extraneous particulatematter from the sampled air and means to transfer charged molecules andclumps of molecules from the sampled air to an inert gas, such transfermeans comprising a first, air guide, passage through which in use theair is passed and a second, inert gas, passage through which an inertgas can be supplied to meet the air at a boundary at which there is aninterface, and means for applying one of an electrical and magneticfield for causing the charged molecules in the air to traverse theinterface into the inert gas, and means for performing spectroscopicanalysis.